US 7142372 B2 Abstract A zoom lens system includes a negative first lens group which is stationary or movable, a positive second lens group which is movable, and a positive third lens group which is movable, in this order from the object.
Upon zooming from the short focal length extremity to the long focal length extremity, a distance between the negative first lens group and the positive second lens group decreases, and a distance between the positive second lens group and the positive third lens group increases.
The zoom lens system satisfies the following conditions:
0.3< fw/|f _{1}|<0.65(f1<0) (1)
0.6< fw/f _{2}<1.2 (2)
0.3< fw/f _{3}<0.6 (3)
wherein -
- fw designates the focal length of the entire zoom lens system at the short focal length extremity; and
- f
_{i }designates the focal length of the i^{th }lens group (i=1, 2, 3).
Claims(5) 1. A zoom lens system comprising a negative first lens group which is stationary or movable, a positive second lens group which is movable, and a positive third lens group which is movable, in this order from an object,
wherein upon zooming from the short focal length extremity to the long focal length extremity, a distance between said negative first lens group and said positive second lens group decreases, and a distance between said positive second lens group and said positive third lens group increases; and
wherein said zoom lens system satisfies the following conditions:
0.3< fw/|f _{1}|<0.65(f1<0)0.6< fw/f _{2}<1.20.3< fw/f _{3}<0.6wherein
fw designates the focal length of the entire zoom lens system at the short focal length extremity; and
f
_{i }designates the focal length of the i^{th }lens group (i=1, 2, 3).2. The zoom lens system according to
1.3< m _{2t} /m _{2w}<2.61.1< m _{3t} /m _{3w}<1.6wherein
m
_{it }designates the lateral magnification of the i^{th }lens group (i=2, 3) at the long focal length extremity when an object at infinity is in an in-focus state; andm
_{iw }designates the lateral magnification of the i^{th }lens group (i=2, 3) at the short focal length extremity when an object at infinity is in an in-focus state.3. The zoom lens system according to
wherein said single biconcave lens element satisfies the following condition:
0.3< fw/|r1|<0.65(r1<0)wherein
r
1 designates the radius of curvature of the object-side surface of said single biconcave lens element.4. The zoom lens system according to
wherein said single positive lens satisfies the following condition:
75<ν2 wherein
ν2 designates the Abbe number of said single positive lens element.
5. The zoom lens system according to
wherein said positive lens element and said negative lens element satisfy the following condition:
25<ν _{3p}−ν_{3n} wherein
ν
_{3p }designates the Abbe number of said positive lens element of said third lens group; andν
_{3n }designates the Abbe number of said negative lens element of said third lens group.Description 1. Field of the Invention The present invention relates to a zoom lens system for an electronic still camera (digital camera) having a wide angle-of-view (i.e., a shorter focal length at the short focal length extremity) and a zoom ratio of approximately 3. 2. Description of the Prior Art In recent years, a digital camera is not only used as a camera per se, but also provided in a portable data handset (PDA: Personal Digital Assistant) and a mobile phone, etc. An imaging device (imaging module), such as a CCD and a CMOS, used for such a digital camera has been required to be very much miniaturized. Therefore an imaging device with a relatively smaller effective imaging area has often been used; and there have been many digital cameras whose optical system is constituted by a smaller number of lens elements. As a small-sized zoom lens system which has a smaller number of lens elements, a negative-lead type lens system has been frequently employed. In such a lens system, there are at least two advantages, i.e., (i) the focal length of the lens system can be made shorter at the short focal length extremity, and (ii) telecentricity on the image side can be maintained. For example, the following Japanese Unexamined Patent Publications (hereinafter, JUPP) have disclosed a negative-lead type lens system of three (and two)-lens-group arrangement, and drawbacks thereof will be discussed hereinafter: JUPP No.2002-55278, JUPP No.Hei-11-237549, and JUPP No.Hei-10-513270. In JUPP No. 2002-55278, a zoom lens system of a three-lens-group arrangement has been disclosed, i.e., a first lens group having a negative refractive power (hereinafter, a negative first lens group), a second lens group having a positive refractive power (hereinafter, a positive second lens group), and a third lens group having a positive refractive power (hereinafter, a positive third lens group), in this order from the object; and the third lens group has a weaker positive refractive power (hereinafter, positive power). However, zooming is mainly performed by the first lens group and the second lens group. As a result, the third lens group does not substantially contribute to zooming, so that the zoom lens system has not sufficiently been miniaturized. In JUPP No. Hei-11-237549, a zoom lens system of a three-lens-group arrangement has been disclosed, i.e., a negative first lens group, a positive second lens group, and a positive third lens group, in this order from the object; and the power of each lens group is weak, and the power of the second lens group is particularly weak. Consequently, the distance between the first lens group and the second lens group becomes longer, so that the overall length of the zoom lens system becomes longer. In JUPP No.Hei-10-513270, a zoom lens system of a three-lens-group arrangement has been disclosed, i.e., a negative first lens group, a positive second lens group, and a positive third lens group, in this order from the object; and the power of the positive second lens group is weak, so that the zoom ration is less than two. Consequently, this publication is not worth discussing on whether the entire optical system is longer or shorter. If an attempt is made to make the overall length of the zoom lens system shorter, it is understood that the power of each lens group is made stronger so that the traveling distances of the lens groups become shorter. However, if the power of a lens group is made stronger, aberrations become larger. Consequently, it becomes difficult to correct aberrations suitably over the entire zooming range. The present invention, with consideration of the above-described drawbacks, provides a small-sized and high-quality zoom lens system having a negative lens group, a positive lens group and a positive lens group, in this order from the object. According to an aspect of the present invention, there is provided a zoom lens system including a negative first lens group which is stationary or movable, a positive second lens group which is movable, and a positive third lens group which is movable, in this order from the object. Upon zooming from the short focal length extremity to the long focal length extremity, a distance between the negative first lens group and the positive second lens group decreases, and a distance between the positive second lens group and the positive third lens group increases. The zoom lens system satisfies the following conditions:
wherein fw designates the focal length of the entire zoom lens system at the short focal length extremity; and f Both further miniaturization of the zoom lens system and higher performance thereof can be attained by suitably distributing refractive power (hereinafter, power) over each lens group so that conditions (1) to (3) are satisfied. The zoom lens system preferably satisfies the following conditions:
wherein m -
- m
_{iw }designates the lateral magnification of the i^{th }lens group (i=2, 3) at the short focal length extremity when an object at infinity is in an in-focus state.
- m
The negative first lens group is preferably constituted by a single biconcave lens element which satisfies the following condition:
wherein r The positive second lens group is preferably constituted by a single positive lens element which satisfies the following condition:
wherein ν2 designates the Abbe number of the single positive lens element. The positive third lens group is preferably constituted by a positive lens element and a negative lens element which can be bonded, or may not be bonded. The positive lens element and the negative lens element satisfy the following condition:
wherein ν ν The present disclosure relates to subject matter contained in Japanese Patent Application No. 2003-323657 (filed on Sep. 16, 2003) which is expressly incorporated herein in its entirety. The present invention will be discussed below in detail with reference to the accompanying drawings, in which: The zoom lens system of the present invention, as shown in the lens-group moving paths of Upon zooming from the short focal length extremity (W) to the long focal length extremity (T), the negative first lens group In A diaphragm in which the diameter of the opening (aperture) is invariable (hereinafter, simply referred to as a diaphragm) is provided in the close vicinity of at least one of the most object-side surface and the most image-side surface of the positive second lens group Focusing is performed by moving at least any one of the negative first lens group The negative first lens group Condition (1) specifies the ratio of the focal length of the entire zoom lens system at the short focal length extremity to the focal length of the negative first lens group If fw/|f If the negative refractive power of the negative first lens group Condition (2) specifies the ratio of the focal length of the entire zoom lens system at the short focal length extremity to the focal length of the positive second lens group The positive second lens group If the positive refractive power of the positive second lens group If the positive refractive power of the positive second lens group Condition (3) specifies the ratio of the focal length of the entire zoom lens system at the short focal length extremity to the focal length of the positive third lens group In addition to the zooming function, the positive third lens group If fw/f If the positive refractive power of the positive third lens group As explained, the positive second lens group Condition (4) specifies the ratio of the lateral magnification of the positive second lens group Condition (5) specifies the ratio of the lateral magnification of the positive third lens group Conditions (4) and (5) are provided for the purpose of achieving both further miniaturization of the zoom lens system and higher optical performance thereof. If the positive second lens group Likewise, if the positive third lens group Due to the above drawbacks, the traveling distance of each lens group cannot be well balanced, so that the overall length of the zoom lens system becomes longer. For the purpose of further miniaturization of the zoom lens system, the negative first lens group Furthermore, in order to make (i) the diameter of the negative first lens group Condition (6) specifies the radius of curvature of the most object-side surface of the negative first lens group If the radius of curvature becomes larger to the extent that fw/|r If fw/|r For the purpose of achieving further miniaturization of the zoom lens system and cost reduction, the positive second lens group If the Abbe number of the glass material of the single positive lens element constituting the positive second lens group In the positive third lens group If the difference of the Abbe numbers becomes smaller to the extent that ν At least one lens surface among the lens surfaces of the positive second lens group Specific numerical data of the embodiments will be described hereinafter. In the diagrams of chromatic aberration (on-axis chromatic aberration) represented by spherical aberration, the solid line and the two types of dotted lines respectively indicate spherical aberrations with respect to the d, g and C lines. In the diagrams of lateral chromatic aberration, the two types of dotted lines respectively indicate magnification with respect to the g and C lines; however, the d line as the base line coincides with the ordinate. In the diagrams of astigmatism, S designates the sagittal image, and M designates the meridional image. In the tables, F In addition to the above, an aspherical surface which is symmetrical with respect to the optical axis is defined as follows:
- c designates a curvature of the aspherical vertex (1/r);
- y designates a distance from the optical axis;
- K designates the conic coefficient;
- A4 designates a fourth-order aspherical coefficient;
- A6 designates a sixth-order aspherical coefficient;
- A8 designates a eighth-order aspherical coefficient; and
- A10 designates a tenth-order aspherical coefficient.
[Embodiment 1]
The negative first lens group The positive second lens group The positive third lens group The symbol CG designates a cover glass (a filter group provided in front of the imaging device). A diaphragm having an a radius of 1.06 is provided on the object-side of the positive second lens group In regard to the lens-group moving paths of
Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):
[Embodiment 2] A diaphragm having a radius of 0.97 is provided on the object-side of the positive second lens group The basic lens arrangement is the same as the first embodiment. In regard to the lens-group moving paths of
Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):
[Embodiment 3] A diaphragm having a radius of 0.89 is provided on the object-side of the positive second lens group The basic lens arrangement is the same as the first embodiment; however, the positive lens element and the negative lens element constituting the positive third lens group In regard to the lens-group moving paths of
Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):
[Embodiment 4] A diaphragm having a radius of 1.12 is provided on the object-side of the positive second lens group The basic lens arrangement is the same as the first embodiment. In regard to the lens-group moving paths of
Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):
The numerical values of each condition of each embodiment is shown in Table 5.
As can be understood from Table 5, each embodiment satisfies each condition. Furthermore, the various aberrations are well corrected. According to the above description, a small-sized and high-quality zoom lens system, which (i) is constituted by a negative lens group, a positive lens group and a positive lens group, in this order from the object, and (ii) has a shorter focal length at the short focal length extremity, can be obtained. Patent Citations
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